The present invention concerns apparatus and a method for processing video signals to implement a plurality of signal processing functions in a single operation, and in particular to apparatus which uses a neural network to perform these functions.
In many signal processing systems, functions are applied to data sequentially. That is to say one function is applied to the input data and the output values produced by that function are applied as the input values to the next function. This type of processing is commonly referred to as pipeline processing.
An exemplary system which employs pipeline processing is a video camera. One such camera is described in an article by K. A. Parulski et al. entitled "A Digital Color CCD Imaging System Using Custom VLSI Circuits," IEEE Transactions on Consumer Electronics, Vol. 35, No. 3, pp. 382-389, August, 1989.
The camera described in this paper employs a CCD sensor which collects samples representing successive video images. These samples are then digitized and processed by a color filter array (CFA) signal processor and a red, green, blue (RGB) signal post-processor. The CFA processor generates, from the single image samples provided by the CCD device, a complete set of Red (R), Green (G) and Blue (B) samples. In addition, the CFA processor performs color balance corrections on the RGB signals. The RGB post-processor performs black-level adjustments, gamma correction and aperture correction.
As described in the referenced article, the circuitry used to perform these processing functions is implemented in two VLSI integrated circuits. These circuits represent a relatively large amount of special purpose circuitry produced only after an expensive development cycle.
In addition to requiring a relatively large amount of special purpose circuitry, systems such as that shown in the referenced paper introduce a delay in their processing paths due to the pipelining of the signal processing operations. Parallel signal processing paths may exist in the system, for example, if audio information from the observed scene were being processed in parallel with the video information. The delays caused by the pipeline processing of the video information are desirably compensated for in the audio signal processing circuitry.
While the delays for the referenced video camera processing circuitry are relatively small, other video signal processing apparatus may employ one or more frame delay elements in its processing circuitry. These elements introduce more substantial delays for which compensation is more difficult.
Furthermore, in systems of the type described in the referenced article, there is an inherent conflict between the precision of the design and its cost, as reflected by its complexity. Many of the processing steps performed in a video camera are modeled as relatively simple mathematical functions, even though these functions do not strictly conform to the desired processing steps. These functional models are used only because it would not be cost effective to implement the desired processing steps according to a more rigorous model or to implement multiple independent functions as a single model.